Along with a so-called “8020 campaign” (improvement in dental health, preservation of dentin (MI: Minimal Intervention)) to try to keep 20 or more own teeth even when being 80 years old, the ratio at which many teeth remain in aged persons have rapidly increased. In association with this, however, a problem of dentin exposure due to new dental diseases (e.g., wear of teeth, alveolar bone loss caused by periodontal disease, etc.) has arisen. Exposed dentin is not good in caries resistance because unlike the enamel, tissues constituting the dentin is low in mineral concentration, and the exposed dentin may cause development of, for example, hyperesthesia when a dentinal tubule comes to be open by the action of an acid in an oral cavity. As a method of improving this, there have been known a method of coating with a polymeric material and a method of applying two materials alternately to make an inorganic salt deposit to form a physical barrier, thereby closing dentinal tubules. However, these methods have a problem that a cover is worn by a toothbrush or the like to be broken easily because only a surface or a shallow portion near openings of dentinal tubules are covered. Moreover, although being a material with high biocompatibility, there has been another problem with it that application of the material makes a plaque adhere, causing inflammation and root caries.
On the other hand, a calcium phosphate cement (hereinafter sometimes abbreviated as “CPC”) in which tetracalcium phosphate (hereinafter sometimes abbreviated as “TTCP”) and dicalcium phosphate anhydrous (hereinafter sometimes abbreviated as “DCPA”) has been known as a calcium phosphate composition having setting property, which has been reported to be converted, within a living body and within an oral cavity, gradually into a bioabsorbable hydroxyapatite (hereinafter sometimes abbreviated as “HAp”; Ca10(PO4)6(OH)2) which can further unite with a biological hard tissue with its form maintained.
For example, Japanese Patent No. 3017536 (patent document 1) discloses that a calcium phosphate composition including tetracalcium phosphate and dicalcium phosphate anhydrous reacts in the presence of water to form hydroxyapatite. It has been reported that the thus obtained hydroxyapatite can replace bone gradually when it comes into contact with a biological hard tissue, and the aforementioned calcium phosphate composition is usable as a remineralizing agent because it possesses remineralization potential. On the other hand, it has been disclosed that an alkali metal salt of phosphoric acid, such as disodium hydrogen phosphate (Na2HPO4), is added in order to achieve rapid setting of the above-mentioned calcium phosphate composition. However, it has been neither disclosed nor suggested that an alkali metal salt of phosphoric acid is added for the purpose of improving the effect of mineralization.
JP 1-163127 A (Patent Document 2) discloses a composition for recovery from hyperesthesia comprising tetracalcium phosphate, calcium phosphate having a Ca/P molar ratio of less than 1.67, and a thickener. This reports that the composition can reduce hyperesthesia when it is applied to a hyperesthetic site of a tooth and held for a prescribed time. The reason for such remarkable reduction in hyperesthesia is believed that calcium ions or phosphate ions eluted from a kneaded mass of such a composition with water or the like diffuse and penetrate into dentinal tubules, then hydroxyapatite deposits in the dentinal tubules, so that external mechanical stimulation, thermal stimulation, and chemical stimulation are intercepted. On the other hand, it is also disclosed that other ingredients, such as hydroxyapatite, calcium fluoride, titanium oxide, calcium hydroxide, sodium phosphate, ammonium phosphate, alumina, and silica, may be added to the aforementioned composition for hyperesthesia treatment in order to adjust kneadability with water or paste viscosity. However, it has been neither disclosed nor suggested that an alkali metal salt of phosphoric acid is added for the purpose of improving the effect of mineralization.